Multi-coat coating systems are well known in the coatings industry for coating a variety of substrates ranging from wood, plastics and composites to metal. U.S. Pat. No. 3,639,147 describes such a system for use in coating motor vehicles. Multi-coat coating systems provide metallic substrates with both the requisite protection from corrosion and marring and with pleasing decorative qualities. These two functions of coating systems are particularly important in the automobile industry where the underlying metal substrate is subjected to rigorous environmental conditions and where the appearance of the finished article is one of the most important selling features. Advances in electrocoat primer coatings have vastly improved the corrosion resistance of automobiles, while similar advances in finish coatings have provided striking new color effects and improved weather, sun, and mar resistance.
Recent years have seen the introduction of metallic, pearlescent and opalescent color effects in finish coatings for automobiles. Metallic effects, in which the appearance of sparkle is imparted to finish coatings, are generally achieved by the introduction into one or more layers of a multi-coat coating system of finely divided metallic flake or mica particles. The widespread use of aluminum pigments to produce so-called "metallic" effect finishes in automotive products began in the early 1960's and has grown steadily since. It is estimated that today more than seven out of ten automobiles manufactured has a metallic effect paint finish which incorporates aluminum and/or micaceous flake pigments. When these coatings or paint finishes for automobiles employ aluminum flake pigments, the aluminum which is used is one of the so-called "non-leafing" grades of aluminum flake. Non-leafing grades of aluminum flake are milled with appropriate milling aids which cause the flake to distribute throughout the finish coating with random orientation of the flake surfaces to produce the "sparkle" so characteristic to metallic finishes. Typical systems of this type are disclosed in U.S. Pat. Nos. 4,048,136; 4,499,143; and 4,605,687.
The Variety of rich and lustrous colors which have been made available through these metallic, opalescent, and pearlescent automotive finish coatings has whetted the appetite of the automotive consuming public. Accordingly, although multicoat coating systems have been in use for many years in the automotive industry, the art is in constant search of coating systems possessing novel or unique color effects which, at the same time, have the requisite durability, high gloss, and good color maintenance.
However, the use of so-called "leafing" grades of aluminum pigments has not been widespread in automotive finish products. Leafing aluminum flake is milled with a fatty acid lubricant to produce flake which tends to orient generally parallel to the underlying substrate surface and to aggregate in a layer close to the upper surface of the coating film. Because of this tendency to aggregate close to the surface of the paint coating, paints which contain leafing aluminum have a tendency to chalk or rub off. Moreover, the fatty acid lubricant coating on the aluminum flake can provide a site for delamination if subsequent coatings are applied. For these reasons, leafing aluminum paints have been generally restricted to such applications as reflective roofing materials, bridge and structural steel corrosion protection, and similar applications. In these applications, the bright, reflective nature and corrosion protective characteristics of leafing aluminum coatings are desirable, while the undesirable tendency of such coatings to chalk or delaminate is not a concern.
It is therefore an object of the present invention to provide a decorative coating system, primarily for use in automotive coatings, which possesses the bright, mirror-like finish of leafing aluminum.
It is a further object of the present invention to provide a decorative coating system, primarily for use in automotive coatings, in which the silvery reflective effect of the leafing aluminum is color modified by the inclusion of one or more transparent pigmenting agents.
It is a still further object of this invention to provide leafing aluminum-containing multi-layer coating systems which resist delamination.